Infection with human papilloma virus (HPV) is common. HPV can be transmitted sexually, and it is estimated that 20-80% of sexually active adults have been infected. While a majority of infections are asymptomatic, infection can lead to the development of genital warts (which have a prevalence of about 1-5% among adults) and cancer of the anogenital tract. Another type of cancer, cervical cancer, is strongly associated with HPV (Frazer, Genitourin. Med. 72:398-403, 1996). HPV types 6, 11, 16, 18, 31, and 33 are often associated with an increased risk of cancer, with types 16 and/or 18 being detected in more than 90% of cervical carcinomas (van Driel et al., Ann. Med. 28:471-477, 1996). Types 6 and 11 are also associated with anogenital warts. For reviews of papilloma viruses and their associated pathologies, see Shah et al., “Chapter 66: Papillomaviruses,” In: Virology, 3rd Edition, Fields et al., Eds., Raven Press, Philadelphia, pp 2077-2109, 1996, and zur Hausen, J. Natl. Cancer Inst. 92:690-698, 2000.
There is currently no safe and effective way to treat or prevent warts or the diseases described above by targeting the immune system. Efforts to develop such therapies have been hampered for several reasons, one of which is the dogma that antigens from a single HPV type elicit a limited, type-specific immune response. Consequently, it has been suggested that a cocktail containing antigens from several different HPV types is necessary for a broadly effective HPV therapy (Caine et al., Science 288:1753, 2000).